Electronic circuit comprising linear and logarithmic d.c. measuring channels designed for simultaneous operation



Nov. 24, 1970 J. WEILL 3,543,168

ELECTRONIC CIRCUIT COMPRISING LINEAR AND LOGARITHMIC D.C. MEASURING CHANNELS DESIGNED FOR SIMULTANEOUS OPERATION Filed Oct. 16, 1967 United States PatentO M 3 543 168 ELECTRONIC CIRCUI'I" CdMPRISING LINEAR AND LOGARITHMIC D.C. MEASURING CHANNELS 3,543,168 Patented Nov. 24, 1970 ice measuring channel (voltage developed across the terminals of the load resistor) and a second output at-a potential which is equal to the sum of the potential of said first output and of a logarithmic potential (voltage across the terminals of the diode) an operational amplifier whose DESIGlFED FOR SIMULTANEOU? OPERATION. 5 input is coupled directly to said second output, and a Jacky Weill, Saint-Cloud, France, asslgnor to Commlsh rfi t d h h d t sariat a lEnergie Atomique, Saint-Cloud, France parap ase amp 1 er connec e on t 6 one an o l Filed Oct 16 1967 No. 675,375 first output and on the other hand to the input of said Claims priority, application France No 7 19 operational amplifier with the result that the output of 82,816 10 this latter constitutes a purely logarithmic measurlng Int. Cl. G06g 7/24 channel. U 328-445 1 Claim One form of execution of the invention is shown by way of example in the accompanying drawings, in which: FIG. 1 is a schematic diagram of the upstream section of the electronic circuit according to the invention; and ABSTRACT OF THE DISCLOSURE FIG. 2 is a schematic diagram of the complete electronic circuit.

The circuit pfovifies slmultaneous hheal: and toga Referring to FIG. 1, let D designate a detector which Tithmic measuring Channels and e p a detee' supplies a direct current to an amplifier A possessing negawhich pp a current t amPhfieT, a dlode tive feedback of cathode obtained through the resistor ing a logarithmic characteristic, and the complete as- R2 and let V=K 1 i/io, 5 being a constant designate sembly comprises an Output whlch consumes a lmear the law of the current within the diode d (this law being measuring Channel and all Operational amplifier Whose turned to useful account in conventional logarithmic amoutput constitutes a purely logarithmic measuring channel. 1ifi The circuit of FIG. 1 shows that the output voltages V and V have the following values respectively: V =R I This invention is concerned with an electronic circuit V+V1 K1 og U10 RZ/RTFRII) arrangement comprising linear and logarithmic measur- There 15 therefore Phtamed a hhear meafhrlhg Output 1 ing channels which are supplied with direct current and and h h havlhg a POtehtIaI 2 Whleh 18 the Sum of work Simultaneously a logarithmic law and of a linear law. I

It frequently proves necessary in electronics (for ex- In the complete diagram of the device according to the ample for the control of nuclear reactors or for radiamvehtleh G- 2 PataPhase amphhet B has the tion protection) to make use of a logarithmic measuring thhetleh of hflnglng 1 Into p W1th 2 111 other to be channel in conjunction with a linear measuring channel able to deduct f 2 the Potentla1 1 of the hheal in order to derive benefit in one case from the measur- P ehahneh W1th the fihat result that one of the two ing range and from the ease of elaboration of the period outputs 1S a hhear measurement. and t other output and in the other case from the accuracy of measurement (P P the operatlehal amphfiel 1s a P y logaprovided. In point of fact, it would prove an advantage nthmle measurement 3- to be able to take both measurements simultaneously by h aeeordaheewlth a praetteal form f the means of a Single electronic circuit. Not only would this resistors ot the circuit according to the invention are glven achieve an appreciable economy in the installation, but the tonowmg Values: operational safety would also be obtained by virtue of R =l0 ohms, R =5.10 ohms.

a perfectly continuous measurement. R =R ,=Rt,-=R =10 ohms and Rq=1.25.10 ohms and Accordingly, the present invention is specifically in respect of the value K=10- of the constant of the directed to an electronic circuit which takes the two diode d, the followiiig linear and logarithmic responses above-mentioned measurements simultaneously. are obtained with a current which varies from 10- to More precisely, this invention relates to an electronic 10- amp.

IAmps 10- 10- 10- 10- 10- 10- 10- 10- 10- V1 (linear channel in volts) 10- 10- 10- 1 10 V3 (logarithmic channelinvolts). 0 1.25 2.5 3. 75 5 6.25 7.5 8.76 10 circuit comprising linear and logarithmic D.C. measur- Other values are possible and, in particular, by maining channels designed for simultaneous operation, said taining the quantity circuit being characterized in that it comprises a detector R R 1 2 WhlCh supplies a dlrect current having an intensity I to an T amplifier having a load impedance which is constituted by a resistor mounted with negative feedback, a diode having a logarithmic characteristic, and the complete assembly comprises a first output which constitutes a linear constant, it is possible by varying R to obtain a switchover which permits of linear measurement over a wider range.

Compared with the known circuits comprising two measuring channels, the circuit according to the invention offers the advantage of dispensing with a detector, a cable, a high voltage supply, a low voltage supply, a linear amplifier and additionally requires only the two single amplifiers B and C.

It is readily apparent that the two outputs of the circuit can be equipped with triggers.

From the point of view of reliability of operation, some some advantages are to be gained by the use of two separate chains but the device according to the invention en- 4 rents. The application of this principleis useful in radiation protection instruments.

The circuit according to the invention has been tested under the following conditions:

K=0.06 (transistor 2 N 930 mounted as a diode) Gain over amplifier C=10 The above test has led to the following results:

I Amps 10- 10 10-" 10- 1O- 10 10- 10- 10- V (linear calculated volts) 10" 10* 1O- 10- 10' 10 10- 1 10 V1 (linear measured volts) 10- 10- 10-1 1 10 V3 (logarithmic calculalted volts) 1. 2 1. 8 2. 4 3. 3. 3 4. 2 4 8 5. 4 6.0 V3 (logarithmic measured volts)- 1. 2 1. 8 2. 4 3. 1 3. 7 4. 3 4 9 5. 6. 1

from which it is apparent that, in order to comply with the logarithmic law, it is necessary to ensure that The above condition, which can always be fulfilled in practice, must be strictly complied with and governs the choice of one of the resistors R or R It should be noted that the current I is multiplied by the factor This can permit the measurement of smaller currents than those which are usually permitted by the diodes employed. Thus, by means of a diode which is limited to 10- A, it will be possible to measure 10- A by establishing It should be pointed out that, in the case of a small number of decades and especially in the case of weak currents, it can be of interest to employ only the circuit of FIG. 1, this being particularly the case with portable instruments (radiation protection instruments, for example).

In this case, in respect of the values R =10 R =10 i =10 A., K=0.1, we may have the following results:

I Amps. 10-

What we claim is:

1. An electronic circuit providing simultaneously two voltages a first of which is linear and the second of which is logarithmetic with respect to an input current, a first output for said circuit for the first voltage, a second out put for said circuit for the second logarithmetic voltage, an amplifier connected in said circuit, an output for said amplifier, a resistance connected across said input and said output of said amplifier including a diode having a logarithmic characteristic, said first output being connected between said diode and said resistance, an operational amplifier, an input for said operational amplifier connected to the output of said amplifier and receiving the second voltage, a phase-inverting amplifier, an input for said phase-inverting amplifier connected to said first output and receiving said first voltage, an output for said phase-inverting amplifier connected to the input ofsaid operational amplifier and an output for said operational amplifier forming said second output and providing the second logarithmetic voltage. 1

References Cited UNITED STATES PATENTS 3,187,325 6/1965 Waldhauer 330 3,329,836 7/1967 Pearlman 307-229 DONALD D. FORRER, Primary Examiner D. M. CARTER, Assistant Examiner US. Cl. X.R. 

